The invention relates to a coordinated, rotating, electric hand tool apparatus, particularly a drill, a hammerdrill or a combination hammer, and to a method of safe operation thereof.
In the case of large, high-powered, rotating, electric hand tool apparatus, the danger exists of injuring the operator by means of excessive rotation of the housing as the latter is carried along due to the sudden obstruction of the tool as a consequence of the kinetic energy stored in the electric hand tool apparatus. The danger of injury is particularly high if the apparatus is obstructed as it is started, that is, if the tool is obstructed when it is initially switched on.
Usually, the sudden high angular momentum, producing this rotation due to the obstruction, is separated from the blocked tool by slip clutches or safety clutches or is limited with respect to the torque. Frequently, however, the separation is delayed so that, due to the rotational energy already transferred to the housing of the electric hand tool apparatus, an excessively high rotation of the housing can no longer be prevented.
In DE 3128410 A1, the measurement of the torque, acting on the housing over the handle guiding the electric hand tool implement, is known. A safety device, for avoiding the obstruction, jamming and blocking of a tool, is activated when a limiting value is exceeded by the analogous integration of a signal proportional to the torque. The guidance of the electric hand tool apparatus by the operator, necessary to build up the counter-force at the handle, is a disadvantage.
The EP 666148 B 1 discloses a method of and an apparatus for avoiding excessively high torsion angles of electric hand tool apparatus which, using a microcontroller, calculates in advance, from the actual angular acceleration of the housing, the torsional angle of the housing, which is to be expected at a future time and, when a limiting value is exceeded, activates a safety device to prevent this value from being exceeded. When the start of the apparatus is obstructed, it may nevertheless happen in isolated cases, especially when weak power supply systems with a high internal resistance are used, that the acceleration of the rotor of the electric motor, which builds up only slowly in such a case, results in such a slight angular acceleration of the housing, that the torsional angle of the housing, calculated in advance, does not exceed the limiting value and consequently the safety device is not activated.
From DE 19631517 A1, the use of electric motors without collectors and slip rings, the rpm of which can be controlled over motor control electronics, especially the use of switched magnetic reluctance motors in electric hand tool apparatus, as well as the air cooling of the control electronics in the housing, is known.